1. Field of the Invention
This invention relates to denture adhesives and methods of making and using denture adhesives.
2. Description of Related Art
Dentures are usually secured in the mouth using creams or powders having adhesive properties. These powders or creams serve both to adhere the dentures to the gums but also to provide a cushion and sealant between the gums and the dentures to permit a comfortable fit.
Denture adhesives must have acceptable organoleptic qualities and need to be sufficiently strong so that a daily application of the adhesive is sufficient for a full day's use. But, the adhesive must not prevent or hinder denture removal at the end of the day.
Most presently available commercial denture adhesives comprise vinyl alkyl ether/maleic acid (or anhydride) copolymers. This class of compounds was set out as a potential denture adhesive in U.S. Pat. No. 3,003,988 to Germann et al., issued Oct. 10, 1961. That patent is directed to synthetic, water sensitized, but water insoluble, materials comprising mixed, partial salts of lower alkyl vinyl ether-maleic anhydride copolymers for stabilizing dentures. The salts mentioned in the patent are a mixture of (a) calcium and (b) alkalis, including sodium, potassium and quaternary ammonium compounds, in a 1:1 to 5:1 mole ratio. The calcium and alkali materials are added to the copolymer to form the mixed salt.
Others have adopted the use of calcium in combination with alkali (especially sodium) salts of the copolymer of Germann et al. Examples of formulations using this combination are: U.S. Pat. No. 4,980,391 to Kumar et al., issued Dec. 25, 1990; U.S. Pat. No. 5,037,924 to Tazi et al.; and U.S. Pat. No. 4,910,247 to Haldar et al., issued Mar. 20, 1990. European Patent Application No 406,643, filed Jun. 22, 1990, is directed to aluminum, calcium and sodium salts of a lower alkyl vinyl ether/maleic acid copolymer.
These salts, however, have not proven to be fully effective at securing the denture and are susceptible to "washout," the erosion of the adhesive from under the denture during use. As a result, these formulations provided less than the twelve hours of holding power that denture wearers have begun to demand.
In order to provide additional adhesive and cohesive properties, others have turned to zinc and strontium salts. Examples of these salts are found in, for example, PCT application No. WO 92/22280, published Dec. 23, 1992, assigned to Richardson-Vicks, Inc. (the cations may also include calcium cations, sodium cations or both); U.S. Pat. No. 4,758,630 to Shah et al., issued Jul. 19, 1988 (zinc partial salts or strontium partial salts); U.S. Pat. No. 5,073,604 to Holeva et al., issued Dec. 17, 1991 (partial calcium salts in combination with either partial zinc or partial strontium salts); PCT application No. WO 92/10988, published Jul. 9, 1992, assigned to Richardson-Vicks, Inc. (the salts may comprise zinc, strontium, sodium, calcium, magnesium, potassium or ammonium cations and mixtures thereof); and PCT Application No. WO 92/10987, published Jul. 9, 1992, assigned to Richardson-Vicks, Inc. (the salts may include zinc or strontium in combination with sodium and calcium cations).
Moreover, PCT Application No. WO 92/10986 is directed to mixed partial salts of lower alkyl vinyl ether-maleic anhydride copolymers. The salts are zinc or strontium cations with calcium cations.
Salts of vinyl alkyl ether/maleic acid copolymers have also found use outside the denture adhesive field. U.K. Patent Specification No. 1,492,038 filed Sept. 19, 1974, assigned to Smith & Nephew Research, Ltd., is directed to orthopedic bandages comprising a vinyl alkyl ether/maleic anhydride copolymer with zinc, aluminum or magnesium oxides. U.S. Pat. No. 4,138,477 to Gaffar, issued Feb. 6, 1979, is directed to mouth odor control using zinc salts of vinyl alkyl ether/maleic anhydride copolymers. Begala, A. & Strauss, U., "Dilatometric Studies of Counterion Binding by Polycarboxylates," J. Phys. Chem., 76, p 254-60 (1972), investigates the volume changes associated with bonding of hydrogen and magnesium ions to, inter alia, a vinyl methyl ether/maleic anhydride copolymer. And Crisp, S, et al., "Zinc Polycarboxylate Cements: A Chemical Study of Erosion and Its Relationship to Molecular Structure," J. Dental Rsch., 55(2), p. 299-308 (1976), reports on magnesium or zinc salts of lower alkyl vinyl ether/maleic acid copolymers.
Despite the effort put into improving the properties of the copolymer and the salts derived from the copolymers, these formulations do not provide the full measure of adhesion, cohesion, and resistance to washout from beneath the denture necessary for a completely successful product.